Recently, the magnetic recording media mounted on various magnetic storage apparatuses, such external storages of a computer, are expected to exhibit a high recording capacity. For meeting the demands for high recording capacity, it has been required for the magnetic recording medium to reliably exhibit a high recording density and for the magnetic head to reliably float at a low height. To meet these requirements, various compositions and structures have been proposed for the magnetic layer of the magnetic recording medium, various materials for the nonmagnetic undercoating layer, and various materials for the nonmagnetic substrate. It is desirable for the magnetic recording media for digital household appliances now under development to be inexpensive as possible.
For realizing magnetic recording media exhibiting a high recording density and compatible with a low-floating magnetic head, various compositions and structures have been proposed for the magnetic layer of the magnetic recording medium, various materials for the nonmagnetic undercoating layer, and various materials for the nonmagnetic substrate. Although aluminum and glass are the chief materials for the nonmagnetic substrate, a polymer resin substrate, the so-called plastic substrate, has been proposed recently for the nonmagnetic substrate.
Lowering the floating height of the magnetic head can fully utilize the higher recording density in the magnetic recording media, but the magnetic recording media also need to operate reliably for a long period in severe environments. It is also required for the magnetic recording media for digital household appliances now under development to operate reliably for a long period in severe environments. The conditions, under which the magnetic recording media are used, can extend from very cold xe2x88x9240xc2x0 C. to very hot and humid 80xc2x0 C. and 80% (in relative humidity). Some household appliance makers require that the magnetic recording media be working normally for five years under the conditions described above.
Tests conducted of the magnetic recording media, including the plastic substrates presently available, reveal that the media develop film swelling (a kind of film cleavage) when they are exposed to the severe conditions described above. Accordingly, there is a need to provide a magnetic recording medium, that can be used reliably for a long period without causing film swelling under severe environmental conditions. There is also a need for a method of manufacturing such a reliable magnetic recording medium. The present invention addresses these needs.
The present invention relates to a magnetic recording medium and a method of manufacturing such a magnetic recording medium. Specifically, the present invention relates to a magnetic recording medium that can be used as a storage of a computer and a method of manufacturing such a magnetic recording medium. The present invention also relates to a magnetic storage using the magnetic recording medium described above.
The present inventor has discovered that, with extensive and intensive investigations, inclusion of a trench at the vicinity of an edge of a nonmagnetic substrate can prevent or reduce film swelling caused by exposure to severe environmental conditions.
One aspect of the present invention is a magnetic recording medium that has a nonmagnetic substrate, a nonmagnetic undercoating layer on the nonmagnetic substrate, a magnetic layer on the nonmagnetic undercoating layer, a protection layer on the magnetic layer, and a liquid lubricant layer on the protection layer. The nonmagnetic substrate can be made of a plastic resin and can have a trench or channel in the vicinity of the edge thereof. More specifically, the trench can extend along the edge of the nonmagnetic substrate.
Another aspect of the present invention is a method of manufacturing the above described magnetic recording medium. The method includes the steps of providing the plastic substrate for the nonmagnetic substrate and forming the trench along the vicinity of the edge of the plastic substrate.
Another aspect of the present invention is a magnetic storage including the above described magnetic recording medium.
The trench can have a width of 0.1 xcexcm to 1.0 xcexcm, such as 0.5 xcexcm, and a depth of 100 nm or deeper. The trench can be formed in the area within 2 mm from the edge of the nonmagnetic substrate. Moreover, the trench can be formed outside the data area of the nonmagnetic substrate.